In it's simplest form, you use a single transistor with the lamp in it's collector. You provide enough base current through a fixed resistor to turn the transistor on and the lamp lights. An LDR has a resistance that drops when light falls on it so wire it between the transistor base and ground. In daylight the low resistance will pull the bias current to ground and turn the lamp off, in darkness it will have no effect so the lamp will light.
Actual values depend on the voltage and how much current the lamp passes and the LDR characteristics of course.
I have just built a unit for my home that turns battery powered lights on when the main electicity fails but only if it is also dark outside.
Brian.